Activating mechanism for hydraulically operable downhole tool

ABSTRACT

An activating mechanism for a hydraulically operable downhole tool provided in a drill string, in which the mechanism is incorporated in the drill string and has a tubular housing, a pressure piston mounted for linear reciprocating movement in the housing between first and second end positions, a mandrel coupled with the piston for movement therewith between an activating position and a non-activating position to control the supply of hydraulic pressure fluid to operate the downhole tool when the mandrel is in the activating position, a cam arrangement for controlling the linear movement of the piston, and a cam follower to permit linear indexing movement of the piston, communication means for applying drill string pressure to the piston, and means biasing the piston in a direction from the second end position to the first end position so that, when drill string pressure is released, the activating mechanism is indexed.

This invention relates to an activating mechanism for a hydraulically operable downhole tool provided in a drill string.

Examples of downhole tool which the activating mechanism of the invention can control include an under-reamer, a stabiliser and a circulating tool. It should be understood, however, that the invention has general application to the control of the operation of hydraulically operated downhole tools, in which reciprocating linear movement of a mandrel can control the pressurisation and de-pressurisation of the tool between activated and deactivated phases of operation.

SUMMARY OF INVENTION

According to the invention there is provided an activating mechanism for a hydraulically operable downhole tool provided in a drill string, in which the mechanism is adapted to be incorporated in the drill string and comprises:

a tubular housing;

a pressure piston mounted for linear reciprocating movement in the housing between first and second end positions;

a mandrel coupled with the piston for movement therewith between an activating position and a non-activating position, in which the mandrel controls the supply of hydraulic pressure fluid to operate the downhole tool when the mandrel is in the activating position;

a cam arrangement for controlling the linear movement of the piston and having a cylindrical cam with a cam profile, and a cam follower engageable with the cam profile such that, upon relative rotation taking place between the cam and the cam follower, linear indexing movement of the piston is permitted between the first and second end positions;

communication means for applying drill string pressure to the piston to move the piston from the first end position to the second end position when permitted by the cam arrangement; and

means biassing the piston in a direction from the second end position to the first end position so that, when drill string pressure is released, the activating mechanism is indexed whereby, upon subsequent pressurisation of the drill string, the earn arrangement does not undergo relative rotation and linear movement of the piston from the first end position is prevented.

In a preferred arrangement, the cam arrangement comprises a cylindrical body which is fixed relative to the drill string, and having at least one inwardly extending indexing pin forming said cam follower, and a cylindrical barrel is rotatable within said cylindrical body and is provided on its outer surface with said cam profile which is engageable by said indexing pin.

The cam profile may be a wavy profile undulating laterally of the direction of linear reciprocation of the piston.

In a preferred arrangement, two axially spaced indexing pins are provided, extending inwardly of the cylindrical body, and engaging a common cam profile at axially spaced locations therealong.

The preferred form of biassing means urging, or tending to urge the piston from the second end position towards the first end position, may take the form of a compression spring.

A preferred embodiment of activating mechanism according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1 a,b and c are longitudinal sectional views of the activating mechanism incorporated in a drill string, and arranged to control hydraulically the operation of a downhole tool, and showing successive stages of activation of the mechanism between the non-activated mode shown in FIG. 1 a and the fully activated mode shown in FIG. 1 c; and

FIG. 2 is a detailed view of a cam profile provided on the outer surface of a rotatable barrel cam forming part of a cam arrangement to control the linear reciprocation of the mechanism.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, an activating mechanism according to the invention is designated generally by reference 10 and is incorporated in a top sub 11 which forms a tubular housing in which the components of mechanism are mounted, and which is adapted to be incorporated in a drill string. A “bottom sub” 12 has a hydraulically operable downhole tool mounted therein, and in the illustrated arrangement only this takes the form of an under-reamer 13 having reamer blades 14 which are capable of moving between withdrawn inoperative positions shown in the drawings, and radially outwardly projected operative positions (not shown) for engagement with the surrounding formation when required.

It should be understood that under-reamer 13 is shown by way of example only, and that the activating mechanism of the invention can be used in order to control hydraulically the operation of other downhole tools, such as a stabiliser or a circulating tool, and in which reciprocating linear movement of a mandrel controls the pressurisation and de-pressurisation of the tool between activated and de-activated phases of operation.

Within the tubular housing 11, a pressure piston 15 is mounted for linear reciprocating movement between a first upper end position shown in FIG. 1 a, and a lower second end position shown in FIG. 1 c.

A mandrel 16 is coupled with the piston 15 for movement therewith, between an activating position shown in FIG. 1 c, and a non-activating position shown in FIG. 1 a.

The mandrel 16 controls the supply of hydraulic pressure fluid to operate the under-reamer 13 when the mandrel is in the activating position, and this is achieved by conveying fluid pressure to operate the under-reamer via an activation port 17.

It can seen from FIG. 1 a that the activation port 17, in the non-activation position, is located above an upper seal 18, and therefore pressure fluid can not flow to operate the under-reamer 13. FIG. 1 b shows an intermediate position of the activation port 17 relative to the seal 18, whereas FIG. 1 c shows the activation port 17 located below the upper seal 18 so that fluid pressure can act on a spring-like wavy actuator 19 of the under-reamer 13, to urge the reamer blades 14 radially outwardly to the operative position.

A cam arrangement is provided to control the linear movement of the piston 15, and has a cylindrical cam with a cam profile, and a cam follower engageable with the cam profile such that, upon relative rotation taking place between the cam and the cam follower, linear indexing movement of the piston 15 is permitted between the first and second end position.

In the illustrated embodiment, the cam arrangement takes the form of a cylindrical body 20 which is fixed relative to the drill string, and which is provided with at least one inwardly projecting indexing pin 21, so as to form the cam follower. The cam profile is preferably provided on the outer surface of a rotatable barrel 22 provided on its cylindrical outer surface with a wavy cam profile 23, as shown in the detail of FIG. 2.

The two indexing pins 21 each engage the cam profile 23, and the axial spacing between the indexing pins 21 corresponds to the wavelengths between successive peaks mid troughs of the cam profile 23 shown in FIG. 2.

Communication means is provided to apply drill string pressure to the piston 15, to move the piston from the first end position of FIG. 1 a to the second end position of FIG. 1 c, when permitted by the cam arrangement. The communication means includes annular port 24, and internal routing within the mechanism which conveys the drill string pressure so as to be applied to the top surface 25 of piston 15.

Biassing means is provided to bias the piston 15 in a direction from the second end position of FIG. 1 c to the first end position of FIG. 1 a so that, when drill string pressure is reduced, the activating mechanism 10 is indexed whereby, upon subsequent pressurisation of the drill string, the cam arrangement does not undergo relative rotation and linear movement of the piston from the first end position subsequently is prevented. In the illustrated embodiment, the biassing means takes the form of compression spring 26 acting upwardly on the lower end of mandrel 16.

The preferred embodiment of activating mechanism disclosed herein can operate an under-reamer tool, as one example only of a hydraulically operated downhole tool. The mechanism utilises a barrel cam to activate and de-activate the tool. An indexing mechanism therefore controls a pressure activated mandrel between one position and a second position, and then back to the first position. By utilising the barrel cam, indexing pins on the body protrude into the barrel cam, that rides on the outside of the inner mandrel. It controls the movement of the mandrel by the pattern of the machine that grooves in the rotating barrel cam.

By utilising the barrel cam indexing mechanism, a control mechanism is provided which operates in basically the same way as known clutch mechanisms.

The barrel cam system disclosed herein basically works as follows:

Drill string pressure is applied to the pressure piston 15 via annular port 24. The pressure of the drill string activates the top 25 of the pressure piston 15, which forces the piston down. When the pressure is released, the spring 26 pushes the system back to the neutral position. The mechanism therefore controls the movement of the activation ports 17 between an activated position and a de-activated position. When the activation ports 17 are allowed to shift past the main upper seals 18, the tool will activate, and this can be an under-reamer, stabiliser, circulating tool, or a number of other different hydraulically operated downhole tools.

When the pressure is released, the spring 26 pushes the tool closed, and the mechanism indexes so that when pressure is applied again, the barrel cam arrangement restricts the movement of the mandrel 16 so that the ports 17 do not overcome the main upper seals 18.

Thus, the barrel cam can only rotate with inward and outward movement of the mandrel. When pressure is applied, the barrel can will track through the pins and control the downward movement of the mandrel. When there is no pressure, the spring takes over, and urges the mandrel back thereby causing rotation of the barrel cam.

When pressure is again applied, the mandrel moves down, and the barrel cam rotates to the alternate position (barrel cam movement plus or minus 90° per cycle). The pattern of the barrel cam is designed so that, at alternate cycles, the tool will be locked in an activated or de-activated position when pressure is applied which is sufficient to overcome the spring pushing on the mandrel. 

1. An activating mechanism for a hydraulically operable downhole tool provided in a drill sting, in which the mechanism is adapted to be incorporated in the drill string and comprises: a tubular housing; a pressure piston mounted for linear reciprocating movement in the housing between first and second end positions a mandrel coupled with the piston for movement therewith between an activating position (FIG. 1 c) and a non activating position (FIG. 1 a), in which the mandrel controls the supply of hydraulic pressure fluid to operate the downhole tool when the mandrel is in the activating position; a cam arrangement for controlling the linear movement of the piston and having a cylindrical cam with a cam profile, and a cam follower engageable with the cam profile such that, upon relative rotation taking place between the cam and the cam follower, linear indexing movement of the piston is permitted between the first and second end positions; communication means for applying drill string pressure to the piston to move the piston from the first end position to the second end position when permitted by the cam arrangement; and means biassing the piston in a direction from the second end position to the first end position so that, when drill string pressure is released, the activating mechanism is indexed whereby, upon subsequent pressurisation of the drill string, the cam arrangement does not undergo relative rotation and linear movement of the piston from the first end position is prevented.
 2. A mechanism according to claim 1, in which the cam arrangement comprises a cylindrical body having at least one inwardly extending indexing pin forming said cam follower, and a cylindrical barrel rotatable within said cylindrical body and provided on its outer surface with said cam profile which is engageable by said indexing pin.
 3. A mechanism according to claim 1, in which the cam profile is a wavy profile undulating laterally of the direction of linear reciprocation of the piston.
 4. A mechanism according to claim 3, in which two axially spaced indexing pins are provided, engaging a common cam profile at axially spaced locations.
 5. A mechanism according to claim 1, in which the biassing means comprises a compression spring acting on a lower end of the mandrel.
 6. A drill string incorporating a downhole tool and a mechanism according to claim
 1. 